1. Field of the Invention
The present invention relates generally to an upper fabric feed device for a sewing machine, and more particularly to such an upper fabric feed device in which the velocities of feed and presser feet are zeroed or made close to zero when these feet contact or engage a work fabric.
2. Description of Related Art
As a conventional upper fabric feed device for a sewing machine, there is disclosed in U.S. Pat. No. 4,446, 803 a device wherein a feed foot and a presser or holddown foot are connected via respective rods to a triangular or ternary link or lever. To this triangular lever, there are connected a spring-biased arm, and a connecting link which in turn is connected to a slide. The slide is connected to a crank mechanism.
U.S. Pat. No. 4,422,398 shows another conventional upper fabric feed device, in which a first and a second motion mechanism are connected to each other and to a triangular lever. The first motion mechanism is connected via a first connecting link to a bell crank mechanism, which in turn is connected to the triangular lever. The second motion mechanism is connected to a swing arm, which in turn is connected to the first motion mechanism via a second connecting link which has the same length as the first connecting link.
However, the former conventional device requires a guide for slidably guiding the slide, which complicates the device and makes it difficult to fabricate the sewing head. Further, the slide and the guide in the sewing head cannot be sufficiently lubricated since the lubrication inside the sewing head should be effected so as to avoid contamination of the work fabric with a lubricating oil. In this respect, this upper fabric feed device is not suitable for a sewing machine adapted to operate at a high speed.
On the other hand, the latter conventional device which uses the two motion mechanisms and many connecting members including the two equal-length connecting links is inevitably complicated with a large number of components accommodated within the sewing head.